Meaning

adverb to the greatest degree or extent; completely or entirely; (`full' in this sense is used as a combining form)

adverb sufficiently; more than adequately

adverb referring to a quantity

originFrom Middle English fully, fulliche, volliche, from Old English fullīċe (“fully”), equivalent to full + -ly. Compare German völlig (“fully”), Swedish fullt (“fully”).

Etymology from Wiktionary, CC BY-SA 3.0